Sign posts are frequently encountered articles on the right-of-way of roads and highways. The sign posts are placed off of the road on the shoulder area of the right-of-way. The signs attached to the posts carry routing and travel information for motorists, including mileage, route designations, fuel and rest stop information, as well as other signage.
The posts typically are embedded in the ground with a above-ground portion to which the sign attaches. Various anchors have been designed for holding the post securely in the ground. Secure anchoring is necessary, as the signs must withstand the force of wind. A wind transverse to the face of the sign does not impose a significant load on the anchoring of the post. However, wind blowing on the face of the sign, even at an acute angle, imposes a significant load.
In addition to the requirement that highway signs be capable of withstanding high wind force, it is also preferable that the posts detach from the anchor upon sudden high impact, such as during a collision by a motor vehicle. By detaching from the anchor, the above-ground portion of the post and the sign are thrown by the impact away from vehicle. This significantly reduces the potential for damage to the vehicle and opportunity for injury to passengers. Further, separation of the in-ground post and the above-ground post during impact reduces damage to the in-ground post, thereby facilitating re-use of the in-ground post for re-mounting the detached sign.
Break-away sign posts have heretofore been devised for use in holding signs yet detaching during sudden impact. U.S. Pat. No. 4,928,446 describes a break-away post that comprises two elongated channels of a U-shape construction connected together by a cylindrical stud. The stud has a central portion with a groove in the surface that defines a reduced wall thickness. This provides an area of structural weakness. The stud includes four pairs of transversely aligned holes through the wall of the stud. The cylindrical stud is held in the U-shaped channel. Bolts pass through the channels and the stud. Nuts thread on the bolts to securely fasten the channels and the stud together.
During sudden impact by a motor vehicle, the area of weakness shears. The post separates, allowing the sign and the above-ground portion of the post to be thrown away from the vehicle. In an impact other than head-on, however, the channel tends to twist about the longitudinal axis of the post. The force of the impact transfers to the bolts securing the stud to the channels. The bolts have a length of 2 and 1/2 inches. For bolts having a shear strength that exceeds the shear strength of the weakened portion of the stud, the stud shears as with a direct head-on impact. The twisting force causes weaker bolts however to shear before the stud shears. As a consequence, the post may then fail to separate. Instead, the post is shattered between the ground level and the point of impact or is bent downwardly and under the vehicle. Either one increases the potential for damage to the vehicle and injury to passengers. While higher-strength bolts can be used, these are significantly more expensive and highway maintenance programs would incur increased inventory tracking and monitoring costs.
Accordingly, there is a need in the art for an improved break-away sign post that severs near ground level upon sudden impact by a motor vehicle, regardless of the direction from which the impact is applied.